Solid-state imaging devices, which are widely used for video cameras and still cameras or the like, are provided in form of a package, in which an imaging element, such as a CCD or the like, is mounted on a base made of an insulating material, with the photo-detector region being covered by a transparent plate. In order to make the device more compact, the imaging element is mounted on the base as a bare chip. FIG. 10 shows the solid-state imaging device disclosed in JP 2001-77277, which is a conventional example of such a solid-state imaging device.
In FIG. 10, numeral 41 denotes a housing, which is made of a base 41a and frame-shaped ribs 41b formed in one piece by resin-molding. An inner space 42 is formed on the upper side of the housing 41. A die pad 43 positioned at the center of the base 41a and leads 44 positioned below the ribs 41b are embedded in the housing 41. An imaging element chip 45 disposed at the center of the inner space 42 is fixed to the upper side of the die pad 43. The leads 44 include inner terminal portions 44a that are exposed to the inner space 42 at the upper side of the base 41a on the inner side of the ribs 41b and outer terminal portions 44b that are accessible from the bottom side of the base 41a below the ribs 41b. The inner terminal portions 44a and the bonding pads of the imaging element chip 45 are connected by bonding wires 46 made of metal. A transparent sealing glass cover 47 is fixed to the upper surface of the ribs 41b, thus forming a package for protection of the imaging element chip 45.
This solid-state imaging device is mounted on a circuit board with the sealing glass cover 47 facing upward, as shown in FIG. 10, and the outer terminal portions 44b are used to connect it to the electrodes on the circuit board. Although not shown in the drawings, a lens barrel incorporating an imaging optical system, whose relative position to the photo-detector region formed in the imaging element chip 45 is adjusted with a predetermined precision, is mounted on top of the sealing glass cover 47. During the imaging operation, object light that has passed through the imaging optical system incorporated in the lens barrel is focused on the photo-detector region and photoelectrically converted.
A solid-state imaging device with such a configuration is connected by the outer terminal portions 44b exposed at the bottom surface of the housing to electrodes on the circuit board, so that the height and the occupied surface area of the package are smaller than in configurations using a connection with outer leads bent downward from the sides of the housing, thus making it suitable for high-density packaging.
In the technology disclosed in JP 2001-77277A, an upper mold 48 and a lower mold 49 as shown in FIG. 11 are used to resin-mold the housing 41 of the shape shown in FIG. 10. The upper side of the lower mold 49 is flat. The lower side of the upper mold 48 is provided with recessed portions 48a corresponding to the ribs 41b. An inner protruding portion 48b forming the inner space 42 and outer protruding portions 48c forming the outer surface of the ribs 41b are provided at both sides of the recessed portions 48a. The leads 44 and the mold pad 43 are supplied in integrated form as a lead frame 50, and are disposed between the upper mold 48 and the lower mold 49.
By interposing the lead frame 50 between the upper mold 48 and the lower mold 49, a cavity 51 for molding the base 41a is formed between the lower mold 49 and the inner protruding portion 48b of the upper mold 48. In this state, a resin is filled, the mold is opened and the molded product is retrieved, with the base 41a and the ribs 41b forming the housing 41 having their finished form. After the molding, the lead frame 50 is cut at locations positioned at the outer side of the ribs 41b. 
In the solid-state imaging device of this conventional example, the inner space 42 is sealed by the sealing glass cover 47, forming a hermetically sealed space. Therefore, there may be deformations due to pressure fluctuations inside the inner space 42 caused by temperature changes or the like, and the connection between the imaging element chip 45 and the inner terminal portions 44a may be damaged.
Furthermore, the thickness of the inner terminal portions 44a of the leads 44 is about half of the thickness below the ribs 41b, and the lower surface of the inner terminal portions 44a is not exposed at the bottom surface of the base 41a. This shape of the leads 44 may cause the following problems:
In order to embed the leads 44 at the suitable positions, the resin is filled in while the leads 44 are held by the upper and lower molds, and their position is fixed. Therefore, the leads 44 have to be clamped between the upper mold 48 and the lower mold 49. However, as mentioned above, the inner terminal portions 44a of the leads 44 located at the inner space 42, have a thickness that does not reach the bottom surface of the base 41a, so that it is difficult to clamp them with the upper and lower molds.
For this reason, with the technology disclosed in JP 2001-77277A, the leads 44 are positioned by clamping those portions of the leads 44 that are further to the outer side than the outer terminal portions 44b with the lower mold 49 and the outer protruding portion 48c of the upper mold 48. Thus, ultimately, the inner terminal portions 44a are molded while not being clamped between the upper and lower molds. Consequently, it is not possible to attain a condition in which the inner protruding portion 48b of the upper mold 48 is pressed with sufficient force and close contact against the upper surface of the inner terminal portions 44a. Therefore, the generation of a resin burr at the edge of the inner terminal portions 44a cannot be avoided. Due to this resin burr, the connection area of the inner terminal portions 44a may be narrowed considerably, and may result in defective connections.
The following explains how the conventional configuration impedes miniaturization. As shown in FIG. 11, an outer protruding portion 48c is necessary at the outer side of the ribs 41b, in order to form the outer surface of the ribs 41b and finish the outer shape of the ribs 41b when resin-molding. As a result, while it becomes possible to clamp the leads 44 at that portion, the following problems occur.
There is a lower limit for the width of the upper surface of the ribs 41b that is given by the surface area necessary for applying the adhesive for adhering the sealing glass cover 47. That is to say, there is a limit to how small the width of the ribs 41b can be made, and this impedes further miniaturization of the surface area of the semiconductor device. Moreover, when the ribs 41b are molded, a taper (not shown) for mold release has to be provided at the side surfaces, and the presence of this taper also causes an increase of the width of the ribs 41b. 